Fuel cells have been proposed as a power source for electric vehicles and other applications. An exemplary fuel cell has a membrane electrode assembly (MEA) with catalytic electrodes and a proton exchange membrane (PEM) sandwiched between the electrodes. Diffusion media made of porous conductive material may be used on the cathode and anode side to improve cell operation.
Water management is an important concern in operation of fuel cells. For example, water is generated at the cathode electrode based on the electrochemical reactions between hydrogen and oxygen occurring within the MEA. Water is needed for and is depleted by transport of protons from the anode through the PEM to combine with oxidant at the cathode. In addition, the proton conductivity of the PEM is heavily dependent on its state of hydration. For these and other reasons, efficient operation of a fuel cell depends on the ability to provide effective water management in the system, for example to control transport of water away from generation sites on the cathode to prevent flooding, and to cool the fuel cell to prevent overheating.
In part to improve water management, diffusion media have been introduced between the electrodes and impermeable members such as a bipolar plate that separate cells within a stack. Carbon fiber paper is useful in these applications, as it is conductive and can maintain electrical connections in the cell.
Optimum water management calls for a balance of hydrophilic and hydrophobic properties in fuel cell components such as carbon fiber paper diffusion media. Because carbon paper has a relatively low surface energy, and is not readily wetted by water, it would be desirable to provide a method for increasing the hydrophilicity of such material so that it could be adapted for providing better water management and cooling in fuel cells.